Photo-enhanced gas sensing of SnS₂ with nanoscale defects

Recently a SnS₂ based NO₂ gas sensor with a 30 ppb detection limit was demonstrated but this required high operation temperatures. Concurrently, SnS₂ grown by chemical vapor deposition is known to naturally contain nanoscale defects, which could be exploited. Here, we significantly enhance the performance of a NO₂ gas sensor based on SnS₂ with nanoscale defects by photon illumination, and a detection limit of 2.5 ppb is achieved at room temperature. Using a classical Langmuir model and density functional theory simulations, we show S vacancies work as additional adsorption sites with fast adsorption times, higher adsorption energies, and an order of magnitude higher resistance change compared with pristine SnS₂. More interestingly, when electron-hole pairs are excited by photon illumination, the average adsorption time first increases and then decreases with NO₂ concentration, while the average desorption time always decreases with NO₂ concentration. Our results give a deep understanding of photo-enhanced gas sensing of SnS₂ with nanoscale defects, and thus open an interesting window for the design of high performance gas sensing devices based on 2D materials.